Chemostratigraphic correlation within the Grand Banks, with a
view of constraining sandstones for provenance analysis
Ceri Roach, Tim J Pearce & Barry Lees
Chemostrat Ltd
Introduction to the Grand Banks
The Grand Banks of eastern Canada lies in the deep waters offshore Newfoundland and incorporates a
series of rift basins associated with the opening of the North Atlantic Ocean. Mesozoic and Cenozoic
strata rest unconformably on Palaeozoic basement, with the Jurassic and Cretaceous rocks forming the
main source and reservoir units within the area. Despite extensive exploration and discovery within the
Jeanne d’Arc Basin, recent discoveries in the Flemish Pass Basin to the north, have highlighted a
greater oil potential within the area. However, exploration in this northern frontier is hampered by a lack
of well penetrations, whilst the deep water and arctic conditions makes for challenging drilling
conditions. As a consequence, a firm understanding of the regional geology is vital to petroleum
exploration within the area. Furthermore, the need for a greater understanding of the sediment
provenance terrains and pathways active during the Mesozoic is apparent, however, in order to tackle
such an investigation, it is important to firstly have a clear understanding of stratigraphy. To go some
way in addressing this, a chemostratigraphic study was conducted on twenty wells spanning the
Orphan, Flemish Pass and Jeanne d’Arc basins, in addition to wells from the Outer Ridge Complex.
The main aim being to establish a robust chemostratigraphic correlation, which can ultimately be used
to constrain key sandstone bodies, which only then, can be targeted for further provenance
investigation.
Elemental Geochemistry
Inorganic elemental chemostratigraphy involves the characterisation and correlation of rock
successions based on stratigraphic variations in their constituent minerals, or in their proportions of
accessory phases. The technique is particular sensitive to variations in clay minerals, heavy minerals
and lithic components that in turn, can be linked to changes in palaeoclimate and palaeoenvironment,
provenance and periods of volcanism.
The current study utilises inorganic geochemical data acquired via inductively-coupled plasma – optical
emission spectrometry (ICP-OES) and inductively-coupled plasma – mass spectrometry instruments.
Sample preparation and analysis followed the procedures advocated by Jarvis & Jarvis (1992a &
1992b) and resulted in quantitative data being acquired for forty-nine elements, including ten major
elements, twenty-five trace elements and fourteen rare earth elements. The geochemical data were
acquired solely from cuttings material and comprise a variety of siliciclastic lithologies, the majority of
which have a strong calcareous component.
Chemostratigraphic Zonation
The study intervals collectively encompass sediments from the Jurassic Downing, Voyager, Rankin and
Fortune Bay formations, the Cretaceous Hibernia and Dawson Canyon formations and the base of the
Palaeogene Banquereau Formation. However, as no one well incorporates each of the recognised
formations, a composite well section was erected as a reference on which to compare subsequent well
penetrations. The resultant reference section was then subjected to a consistent order of interpretation,
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resulting in the establishment of a hierarchical, chemostratigraphic zonation, which consists of three
chemostratigraphic mega-sequences, ten chemostratigraphic sequences and a total of twenty
chemostratigraphic packages.
The chemostratigraphic divisions are erected from the siltstone and finer grained data and are primarily
founded on elements which can be linked to detrital minerals, thus enabling the correlation to be
extended across the greater study area. In particular, elements such as Nb, Ta and Ti, amongst others,
can be tied to specific heavy minerals, which provide information on sediment provenance. Other
parameters such as V, Fe and Mg can be tied to depositional processes and can be utilised to highlight
any changes in palaeoenvironment, whilst elements such as U and Zn, can be directly tied to TOC
concentrations and can be used to highlight organic rich sections.
Provenance Implications
Lowe et al. (2011) present heavy mineral, U-Pb geochronology and grain morphology and chemistry
data to elucidate sediment provenance within the upper Jurassic to Lower Cretaceous sandstones from
two wells within the Flemish Pass Basin. Comparison of the published heavy mineral data (op. cit.) with
the sandstone geochemical data acquired from the same wells, highlighted the element to mineral
associations of the heavy mineral grains encountered in the basin. This identification allowed the
geochemical data from the sandstone and by extension, the finer grained lithologies, to be used to
assess the vertical and spatial distribution of the heavy mineral grains, which provided information on
provenance as well as sediment input.
Isocon maps (maps that contour based on element concentrations) were constructed from the finegrained geochemical data. The maps use data for Nb, Ti and Ta and thus reflect the distribution of
heavy minerals (e.g. rutile and titanite). Heavy mineral assemblages can be affected by hydrodynamic
conditions, such that the assemblages can be preferentially sorted and winnowed (Morton &
Hallsworth, 1999). As a consequence, heavy mineral assemblages will typically be more abundant
closer to the source of the clastic detritus, with these maps therefore, allowing an inference of sediment
pathways to be made throughout different time slices, even in the finer grained fraction, where more
traditional provenance analyses are generally less effective.
Conclusions
The inorganic geochemical data acquired from the twenty wells allowed for an independent,
chemostratigraphic correlation to be erected, which ultimately tied wells from the Jeanne d’Arc through
to the Flemish Pass and Orphan basins. The fine grained-based correlation can be used to constrain
key sandstone bodies, which only then can be confidently targeted for further provenance work. In
addition, the fine grained geochemical data relating to specific heavy mineral species can be used to
assess provenance and sediment input points active during different time slices within the Mesozoic.
References
JARVIS, I. & JARVIS, K.E., 1992a. Inductively coupled plasma-atomic emission spectrometry in exploration geochemistry. In:
Hall, G. E. M. & Vaughlin, B. (eds), Analytical Methods in Geochemical Exploration. Journal of Geochemical Exploration
Special Issue.
JARVIS, I. & JARVIS, K.E., 1992b. Plasma spectrometry in earth sciences: techniques, applications and future trends. In
Jarvis, I. & Jarvis, K.E. (eds), Plasma Spectrometry in Earth Sciences. Chemical Geology, 9, 1 - 33.
LOWE, D.G., SYLVESTER, P.J. & ENACHESCU, M.E., 2011. Provenance and paleodrainage patterns of Upper Jurassic and
Lower Cretaceous synrift sandstones in the Flemish Pass Basin, offshore Newfoundland, east coast of Canada. The American
Association of Petroleum Geologists Bulletin, v.95, p-1295-1320.
MORTON, A.C. & HALLSWORTH, C.R., 1999. Processes controlling the composition of heavy mineral assemblages in
sandstones. Sedimentary Geology 142, 3-29.
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